Fragile articles that are shipped in cartons are often surrounded with protective packaging and shipping elements such as foams, bubble wrap, corrugated cardboard, shredded paper, styrofoam, etc. The packaging and shipping elements are necessary to prevent harm to the fragile article held within the shipping carton. The packaging and shipping elements prevent or minimize movement of the fragile article within the carton and absorb some shocks that occur when the carton is moved or dropped during shipping.
Rigid polyurethane foam has been used in packaging applications where its low cost and ease of application assist packaging designers. Typically for packaging applications, a product with a higher stiffness, as indicated by a higher IFD25, or the indentation force to a 25% deflection as measured by ASTM 3574, is desired. Rigid foams generally have such higher IFD25. However, due to chemical composition, rigid foams also tend to have poor resiliency. After one impact, the struts in rigid foams are damaged or crushed, do not rebound, and then cannot withstand further impacts.
Flexible foam has also been used in packaging applications, but until recently, such foam has mainly been used in lower load-bearing applications. A good definition for xe2x80x9cflexiblexe2x80x9d foam is that from ASTM 1566: a foam is flexible if a 8xe2x80x3xc3x971xe2x80x3xc3x971xe2x80x3 piece of such foam can wrap around a 1xe2x80x3 diameter mandrel at room temperature without rupture or fracture. Little work has been done to enhance the packaging design using flexible foams. In many applications where a three-dimensional package is desired, individual flexible foam pieces are cut from sheets and glued together to form the required supporting packaging structure. This adds labor and time to the fabrication.
Hinged packaging frames have been formed from rigid polyethylene foam, styrofoam, corrugated cardboard and polyurethane foam. U.S. Pat. No. 5,024,328 shows a foam packing frame and blank wherein a block or sheet of foam is hot wire or die cut to form a series of notches and curves, and then is pulled apart and folded at the notches and curves to form a packaging frame. When this cutting technique is used to form a packaging frame with flexible polyurethane foam, the notched portions lack stability and tend to twist and tear, making the packaging frame difficult to install in place within the carton or around a fragile article.
Sealed Air Corporation produces STRATOCELL foam laminates for packaging applications. The laminates are formed from a sheet of rigid polyethylene foam onto which is laminated a thin polyethylene film. The rigid foam sheet is cut with a blade, but the film is not cut. The cut portion forms a notch and the uncut film forms a bendable or foldable hinge. The laminate sheet may be stored flat. The notch and hinge are bent to desired shape when the laminate is installed into a shipping carton. The rigid polyethylene foam and hinge have greater durability during installation, but lack the softness, resiliency and shock absorption required for some shipping applications. Rigid foams have a very high compressive strength, which makes it impractical to measure IFD25. However, if it were measurable, IFD25 for rigid foams is estimated to be well above 300 lb.
U.S. Pat. No. 5,226,557 discloses as one example a protective packaging in which alternating strips of flexible urethane foam and rigid urethane foam are adhered to a film or corrugated paper backing. The strips are joined together to form a panel. The panel is cut to form V-grooves, but the film or corrugated paper backing is not cut and forms a fold edge or hinge. The ""557 patent emphasizes the importance of combining flexible and rigid materials together to form the protective packing wrap. The strength and rigidity of the rigid material strips are deemed essential for shipping protection and for strength when stacking the cartons.
Other hinged packaging elements that use rigid plastics and rigid foams are shown in U.S. Pat. Nos. 4,869,369; 4,883,179; 4,397,705; and 3,564,811.
One object of the present invention is to form a flexible polyurethane foam packaging element that can be cut or notched to form a hinge so that it can be folded or bent when placed around a fragile article to protect the article within a shipping carton. A second object is to overcome the drawbacks, such as twisting and tearing and lack of stability, associated with prior flexible polyurethane foam shipping elements.
A hinged flexible polyurethane foam packaging and shipping element is formed from a flexible polyurethane foam sheet having a desired thickness and an outer surface to which is adhered or laminated to a polyethylene, polypropylene or urethane film. The flexible polyurethane foam has a density in the range of about 0.7 lbs/ft3 to about 2.8 lbs/ft3 and an IFD25 in the range of about 25 lbs to about 270 lbs. The film has a thickness from about 2 mil to about 125 mil, preferably from about 2.5 mil to about 5 mil. Where the film itself is also foamed, a greater thickness may be used. The foam is cut, such as by the xe2x80x9ckiss-cutxe2x80x9d die cutting technique, through all or substantially all of its thickness. At least a portion of the film is not cut. That uncut film portion forms the repeatably bendable hinge. The cut surfaces of the foam may be separated from one another, which causes a bending at the hinge.
The hinged flexible polyurethane foam packaging and shipping element has advantages over the prior art. The element may be stored flat and the hinge portion or portions bent only when the element is being installed within a shipping carton. The hinges eliminate the need to glue foam sheets together to form a three-dimensional design. The flexible polyurethane foam has desired resiliency for protecting fragile articles. Drop curves, which characterize dynamic shock cushioning characteristics (xe2x80x9cenergy absorptionxe2x80x9d) of materials, show no adverse effects from laminating the foam with a film to form a hinge. The drop curves compare favorably to curves for hinged rigid foam packaging and shipping elements of the prior art, but can be used for packaging applications where resiliency and dynamic cushioning are essential.
In addition, the laminated film offers improved rigidity and stability at the hinged portions, as well as across the entire surface of the element.